Influenza virus binds to the erythrocytes through attachment to cell surface carbohydrates. Specifically, influenza virus envelope protein called hemagglutinin binds to a trisaccharide structure containing sialic acid, galactose and N-acetylglucosamine, and is present as the terminal structure of large carbohydrate units of cell surface glycoproteins and glycolipids. This binding is crucial for viral infection. The design of molecules containing carbohydrate structures that mimick the structures recognized by the hemagglutinin molecules and preferentially bind to the virus should inhibit the influenza virus infection. Thus such molecules may prove to be useful drugs.
In biological systems, the receptor (the hemagglutinin on the virus envelope) and the receptor ligands (the cell surface carbohydrates) are displayed in multiple copies. As a result, the interaction between a virus and the erythrocyte involves multipoint attachments between the receptor and receptor ligands. This is hard to mimick with synthetic molecules. For example, the hemagglutinins present on the influenza virus exist as trimers with three potential binding sites and also in multiple copies. Therefore the synthetic inhibitors should be capable of binding not only to the three binding sites of a single hemagglutinin trimer, but also to the adjacent hemagglutinin molecules as well.
Binding to the adjacent hemagglutinin molecules can be achieved by immobilization of sialic acid structures on a polymer back bone as has been shown, Spaltenstein et al., Am. Chem. Soc., 113, 686-687 (1991). An optimum distance of 55A was proposed for optimum binding by Glick et al, J. Am. Chem. Soc., 113, 4701-4703 (1991). However, these two studies dealt with the preparation of compounds containing only one sugar, namely, the sialic acid. However, studies by Paulson et al, J. Biol. Chem., 264, 9850-9859 (1989) showed that in addition to the sialic acid, other sugars, namely, the galactose and N-acetylglucosamine that are connected to the sialic acid are also important for viral recognition.
Sabesan et al., J. Am. Chem. Soc., Vol. 108, pp. 2068-2080 (1986) teach the combined chemical and enzymatic synthesis of ten sialyloligosaccharides that occur as terminal sequences in glycoproteins and glycolipids. Sabesan et al., J. Am. Chem. Soc., 113, 5865-5866 (1991), disclose demonstration of increased inhibitor potency by low molecular weight, synthetic, bivalent receptor determinants containing the trisaccharide structures for the influenza virus of human isolates. The importance of cluster oligosaccharide effects for binding toward proteins is exemplified.
Spaltenstein et al., J. Am. Chem. Soc., Vol. 113, pp. 686-687 (1991) have prepared polymers containing a cluster of sialic acids by polymerization of acrylic esters of sialosides. It was concluded that polyvalent derivatives of sialic acid are more effective than monomeric ones in inhibiting hemagglutination.
The present invention relates to the design of a hemagglutinin recognition molecule wherein two identical trisaccharide structures (bivalent structures) comprising sialic acid (N-acetylneuraminic acid), galactose, and N-acetylglucosamine are attached to another sugar molecule (anchoring sugar). The bivalent structures are better inhibitors of influenza virus than the monovalent structures. Also, the anchoring sugar has been pended with a functional group that upon modification can be polymerized to a macromolecule capable of inhibiting influenza virus infection.